1. Field of the Invention
The present invention relates to an electrostatic electroacoustic transducer and a method of manufacturing the same, and more particularly to an electrostatic electroacoustic transducer and a method of manufacturing the same applicable to a condenser-type microphone and headphone which use a change in capacitance between a diaphragm and a fixed electrode plate wherein the above-mentioned diaphragm can be attached without being flexed with respect to a holding member.
2. Description of the Related Art
In recent years, electronic devices including a mobile phone are reduced in size and their interior spaces are also small. Many of the above-mentioned small electronic devices include electrostatic electroacoustic transducers, such as a condenser microphone and a capacitor loudspeaker. Therefore, there is an inevitable need for a miniaturized microphone unit or loudspeaker unit.
However, in the above-mentioned electrostatic electroacoustic transducer, the shape of the diaphragm arranged to face a fixed electrode plate is generally designed to have a precise circle. Therefore, when it is installed in the interior space of the above-mentioned electronic device whose cross or vertical section is rectangular, the above-mentioned precise circular shape of the diaphragm is not one that can utilize the above-mentioned interior space efficiently.
In view of such problems, Japanese Patent Application Publication No. 2005-86831 discloses a variable capacitance microphone in which a planform of a microphone unit including a diaphragm is in the shape of an oval (like athletic field track), for example. Further, it also discloses such a variable capacitance microphone which efficiently uses the interior space of the small electronic device as described above. According to the structure of the microphone as disclosed in Patent Document 1, a cross-sectional area of the microphone unit is greater than that of the conventional one which is completely circular. Therefore, as to the interior space of the small electronic device like a mobile phone, the minimum wasted space is occupied in the interior space. Further, since the effective area of the diaphragm is large, it is possible to obtain the effects of increasing the sensitivity of the microphone unit.
Incidentally, as described in Patent Document 1, the diaphragm is adhered to and held by a frame-like holding member (diaphragm plate) in the microphone unit.
However, when the diaphragm is in the shape of an oval, the long sides (which face each other on the minor axis side) of the holding member formed into the shape of an oval according to the diaphragm are deformed or bent towards the diaphragm by the tension of the diaphragm. As a result, the diaphragm is flexed between the long sides, and the tension of the diaphragm is reduced. Therefore, there is a problem that it is difficult to manufacture the transducer having the diaphragm with stable tension.